Engine systems use several methods to warm up engine coolant during operation. For example, FIGS. 1A-C illustrate example schematic exhaust systems previously implemented. In one example shown in FIG. 1A, the exhaust system includes a cooled EGR arrangement that is used to transfer exhaust heat to the engine coolant. However, a cooled EGR has the disadvantage that exhaust heat recovery can only occur when exhaust gas is flowing in the EGR, which limits the amount of exhaust heat recovery available from the system. Another disadvantage is that exhaust heat recovery is only a portion of the exhaust gas flow, which may be as low as 25% or lower in some instances relative to the total exhaust flow. Other examples are shown in FIGS. 1B and 1C that include using a separate exhaust heat recovery heat exchanger and valve assembly, possibly in combination with an EGR cooler. However, while the exhaust heat recovered may be increased compared to FIG. 1A (e.g., via a more full exhaust heat recovery and independence relative to the EGR flow), a separate heat exchanger may be large and difficult to package in a vehicle. In addition, heat exchangers may be heavy and/or expensive, which increases the cost of the vehicle. Moreover, packaging an exhaust heat recovery heat exchanger separately from the EGR cooler may further include placing the additional device remotely from the engine, which reduces the temperature of exhaust gas entering the device during warm-up due to heat absorbed by the thermal mass of the upstream components. This arrangement also has the disadvantage that the available heat recovery during engine warm-up is reduced. Yet another example (not shown) includes using a cooled exhaust manifold to extract heat from the exhaust. However, one disadvantage of this arrangement is that the thermal mass of the exhaust manifold is large, which causes a slow coolant warm-up. Another disadvantage is that both the exhaust gas flow and coolant flow through the exhaust manifold cannot be turned off (e.g., because turning off the coolant flow may cause coolant boiling). Thus, transferring heat from the exhaust to the engine coolant may be made to occur during certain unfavorable situations in which it is preferable not to do so, such as at a high temperature and during high load operation.
The inventors have recognized issues with such approaches and herein describe a system and methods for heating engine coolant by transferring heat from an exhaust flow to the engine coolant via a heat exchanger positioned in an exhaust gas heat recovery line coupled to the EGR cooler responsive to an EGR valve position. In particular, an exemplary EGR cooler combined with an exhaust heat recovery device is presented that allows exhaust gas to transfer heat to engine coolant via a branching pathway of the EGR cooler. That is, an exhaust system configured according to the present disclosure allows exhaust gas to be routed to both an EGR and/or the exhaust gas heat exchanger based on EGR valve actuation. The system further allows for differential actuation of exhaust flows to distribute the exhaust gasses to both the EGR and exhaust heat exchanger, which enables a differential control of the exhaust flows therein and thereby control of the heat transferred to the engine coolant during operation. In this way, the technical result is achieved that heat can be recovered from the exhaust gas regardless of flow through the EGR line while also allowing for increased heat recovery from the exhaust gas. One advantage is that up to 100% of the exhaust flow can be allocated to heat recovery based on control of the differential flow through the EGHR branch of the exhaust gas heat recovery device. Another advantage is that the heat recovery can be turned off under operating conditions in which heat recovery may be detrimental, for example, where maximum cooling is desired. With this arrangement, the engine coolant may be efficiently and expeditiously warmed up, e.g., as quickly as possible, during operation. Furthermore, an exhaust system according to the present disclosure allows for a reduced size, weight and cost when implemented into a vehicle.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.